1. Field of the Invention
The present invention generally relates to a network service control method, in particular, to a network service control method using agents and agent dispatching method used therein.
2. Description of Related Art
Throughout evolution of wireless communications systems, technical challenges associated with implementing wireless communication have always been how to pose a mobile node (MN) as an MN travels from one area to another, irregularly changes its point of attachment to terrestrial radio access point (AP) with which it is communicating wirelessly. Indeed, the most critical factor in achieving good performance for mobility protocols is the design of handoff.
Handoff occurs when an MN moves from one radio AP to another. A mere change of radio AP is called a “Layer 2 (L2) handoff”, which does not involve any Layer 3 (L3) signalling at the IP level. If the new radio access point is associated with a new subnet, i.e., if the MN moves from one subnet to another, a changing in routing occurs and requires a Layer 3 (L3) protocol action. This L3 protocol action is called a “L3 handoff” and usually involves exchange of a series of IP messages that are used to update routing information for the MN.
Refer to FIG. 1, which is an operation flow of a conventional handoff process, an L3 handoff process starts at the time when the mobile node enters a new subnet. Accordingly, the mobile node suffers a long duration of handoff delay because it has to wait a plurality of operations for handshaking and registration processes, which include the steps of (1) sending authentication request to the server of the new subnet (hereinafter, “a visited server”); (2) querying authentication data from the server of the home subnet (hereinafter, “a home server”) by the visited server; (3) returning the authentication data from the home server; (4) determining and responding whether to permit the authentication request; (5) DHCP handshaking process between mobile node and the visited proxy; (6) registration process and (7) re-inviting process. After handoff process completed, data connection between mobile node and a corresponding node is re-established.
For better performance, many methods are provided to shorten the duration of handoff delay. For example, each of the following patents/patent applications, PCT U.S. patent application No. WO2005072183 entitled “Mobility architecture using pre-authentication, pre-configuration and/or virtual soft-handoff”, U.S. Patent Application No. US2005135624 entitled “System and method for pre-authentication across wireless local area networks”, U.S. Pat. No. 6,832,087 entitled “Low latency mobile initiated tunneling handoff”, U.S. Pat. No. 6,907,245 entitled “Dynamic offset threshold for diversity handover in telecommunications system”, and China Patent Application No. CN1574778 entitled “Selective pre-authentication to anticipated primary wireless access points” provides a solution for shortening the duration of handoff delay. However, these methods merely solve problems for single mobile node. Further, handshaking performed between server and mobile node suffers unstable network properties such that improvement of connection quality is limited.